PA4T, PA6T, PA9T, PA10T, PA11T, PA12T, and the like have been known as a highly heat-resistant nylon (polyamides). In the highly heat-resistant nylon, a highly heat-resistant nylon in which a long-chain diamine having at least 9 carbon atoms such as PA9T is used may be directly used as a homopolymer, or may be used in the form of a copolymerized polymer in which a comonomer is used at a small quantity. PA4T and PA6T may not be used alone since they have a very high melting temperature (Tm), and a lower decomposition temperature than a processing temperature thereof. In this case, PA4T and PA6T are to be generally copolymerized to reduce the processing temperature. A single- or long-chain aliphatic diamine, a cyclic aliphatic diamine, a branched aliphatic diamine, a single- or long-chain aliphatic dicarboxylic acid, a cyclic aliphatic dicarboxylic acid, and a branched aliphatic dicarboxylic acid may be used as a comonomer of PA6T. In general, adipic acid, isophthalic acid, and the like have been used.
Particularly, in order to use articles made of such a highly heat-resistant nylon as a material for a UTH (under the hood) engine room for automobiles, long-term heat-resistant stability, in which their certain physical properties may be maintained at a condition of a temperature of about 150° C. or higher, for example, about 200 to about 220° C., and a glass transition temperature (Tg) characteristic at about 120° C. or higher are required. As a method capable of improving the long-term heat-resistant stability of the highly heat-resistant nylon, there is a method of increasing a concentration of an amine group in a polymer compared to a concentration of a carboxylic group. Also, comonomers may be combined to adjust a melting temperature (Tm) to enhance melt processability, and a glass transition temperature (Tg) to maintain physical properties at a high temperature.
Korean Unexamined Patent Application Publication No. 2007-0119646 discloses an semi-aromatic polyamide resin having improved retention stability, hot water resistance, chemical resistance, and adhesivity or compatibility to/with other resins by sealing at least about 10% of molecular chain end groups of the polyamide resin and adjusting the ratio of [end amine groups]/[end acid radicals] to about 6 or more. However, the long-term thermal stability and the glass transition temperature characteristic at about 120° C. or higher may not be maintained only when the concentration and ratio of the end amine groups are maintained at a high level.